1. Field of the Invention
The invention relates to the field of explosive blasting techniques and more particularly, but not by way of limitation, to the use of multiple detonation points in a chain of explosives to reduce burn time and the use of an air gap method and apparatus to reduce the quantity of explosive materials using an undulated plastic liner that is loaded once the liner is in place in a generally cylindrical (i.e. straight-sided) borehole or borehole having irregularities.
2. Description of the Prior Art
In the practice of standard blasting methods, elongated boreholes are drilled into a rock formation which is to be removed. The borehole is then completely filled with explosives including solid, liquid or gelatin chemical compounds, which upon detonation, are converted to intensely hot gaseous compounds that, because of confinement within the borehole, exert tremendous destructive forces against the confining rock which typically yields to these forces and is reduced to rubble.
Prior art is limited by the detonation characteristics of blasting agents. Specifically, the critical diameter necessary for sustaining full order detonation limits the application of prior techniques and products. Methods such as plugging or gapping the powder column (Fitzgibbons, Kang) and Axial Air Gapping (Kang, Robert) are limited in that the method of reducing the quantity of explosives risks either a low order deflagration or a complete shutdown of the detonation.
According to prior art the gap method utilizes sympathetic detonation, the ability of the explosion to jump the gap and re-ignite the adjacent charge or creates an internal gap within the column, leaving enough explosives surrounding the void to sustain detonation. In practical applications this latter limit has not been tested since the Axial Air Gap is less than the proven limits of the sympathetic gap.
In the past, protection against water attack has been provided by containing the water-sensitive blasting agent in metal or other water-proof containers or in plastic bags which may then be lowered into the borehole for detonation. More recently, the blasting industry has developed the practice of using tubular plastic liners or sleeves; thereafter the blasting agent is poured or pumped into the lined hole. Such liners provide additionally prevent the loss of blasting agent. There are, however, certain difficulties and problems associated with the use of plastic borehole liners. Generally, the liner employed comprises a thin-wall material so that it may conform to any irregularities within the borehole and so provide a full compaction of the contained explosive to fill the interstices in the wall of the hole.